1. Field of the Invention
The present invention relates to a solder bonding method and a solder bonding device. In particular, the present invention relates to a solder bonding method and a solder bonding device that are suited for making fine bonding, such as bonding between a bonding pad that is formed on a magnetic head slider and a pad that is formed on a lead frame side.
2. Related Background Art
A connection method is conventionally known, with which electrodes that are objects to be bonded are placed close to each other, the electrodes are made to contact ball-shaped solder (hereinafter called solder ball), and heat and ultrasonic vibration are applied to the solder ball (so-called ultrasonic pressure welding), thus making an electrical connection between the electrodes.
FIGS. 3A and 3B are diagrams of a first conventional example of a bonding device that makes connections between electrodes using a solder ball. FIG. 3A shows an approximate cross sectional view of the device, while FIG. 3B shows a laser profile (laser intensity distribution) in the device.
Referring to FIG. 3A, a nozzle 2 having a tapered shape is provided to a bonding device 1 in the first conventional example. A distal end of the nozzle 2 is made larger than at least the outer diameter of a solder ball 3, which is an object to be melted. It is thus possible to extract the solder ball 3 from the distal end side of the nozzle 2 after the solder ball 3 is sent into the nozzle 2. Further, a laser irradiation portion (not shown) is disposed in a rear end side of the nozzle 2. The solder ball 3 is held between the distal end of the nozzle 2 and an electrode portions 6 that is formed on each of a slider 4 and a flexure 5 which are objects to be bonded. The solder ball 3 can be melted by using laser light 7 emitted from the laser irradiation portion.
The arrangement of the bonding device is not limited to that described above, and different types of bonding devices are also known. FIGS. 4A and 4B show a second conventional example of a bonding device that makes connections between electrodes using a solder ball. FIG. 4A shows an approximate cross sectional view of the device, while FIG. 4B shows a laser profile (laser intensity distribution) 9 in the device.
It should be noted that, in the explanation provided here, identical reference numerals are used to denote members in the second conventional example which are common with those used in the first conventional example.
Referring to FIG. 4A, the nozzle 2 having a tapered distal end and the laser irradiation portion (not shown) disposed above the nozzle 2 are provided in a bonding device 8 of the second conventional example, similar to the first conventional example. However, a distal end opening of the nozzle 2 is formed having a smaller diameter than that of the solder ball 3, and suctioning means (not shown) is connected to an inner portion of the nozzle 2. Operating the suctioning means suctions the solder ball 3 from the distal end side of the nozzle 2, and it is thus possible to hold the solder ball 3 at the distal end of the nozzle 2.
In the bonding device 8 constructed as described above, after suctioning the solder ball 3 from a solder ball supplying device side (not shown), causing the solder ball 3 to move onto the electrode portions 6, the solder ball 3 is melted by using laser radiation, thus making a connection between the electrodes 6.
Incidentally, the following structures are known: a structure in which an optical beam is irradiated through a mask, thus irradiating only those locations where soldering is necessary (refer to Japanese Utility Model Application Laid-open No. 6-41174, for example); a structure in which a solder grains discharging process is performed before a process of irradiating a laser beam to the discharged solder grains and to electrodes (refer to JP 2002-76043 A, for example); and a structure in which a shield gas discharge opening is given a long, thin slit shape, and in which the optical axis of laser light is disposed within the shield gas discharge opening (refer to JP 2003-204149 A, for example).
However, the conventional methods described above have the problems shown below.
In the first conventional example, the solder ball must be extracted from the distal end of the nozzle. Consequently, the inner diameter of the distal end of the nozzle is set larger than the outer diameter of the solder ball. As shown in FIG. 3B, laser light (direct light or indirect light) therefore leaks out from a gap in the periphery of the solder ball, going beyond a region where the electrodes 6 are provided, when a laser is irradiated from the rear end side of the nozzle. Therefore there is a fear in that members in the periphery of the electrode portions 6 (such as polyimide that structures the flexure) may be damaged.
On the other hand, in the second conventional example, the diameter of the distal end of the nozzle example, the diameter of the distal end of the nozzle is set smaller than the outer diameter of the solder ball. Accordingly, it is possible to prevent damage to the members in the periphery of the electrode portions 6 caused by the laser, by irradiating the laser onto only the solder ball. However, no laser is irradiated to the electrode portions 6 (refer to the laser profile 9), and thus the temperature of the electrode portions 6 does not rise sufficiently. Consequently, the wettability of the melted solder ball worsens, and there is a fear that the reliability of the connection between the electrode portions 6 will decrease.
A variety of potential problems exist with connections made by using solder balls with the two bonding devices described above. A bonding device and a bonding method that make it possible to heat only an inner side of the region where the electrode portions 6 provided are therefore desired in order to increase the bonding reliability.
A device with which laser light is irradiated to an object by using a mask or the like is shown in the conventional techniques described above. However, neither of the techniques described above discloses a structure that reliably performs laser irradiation over an irradiation range inside the region where the electrode portions 6 is provided.